Thermodynamic and exergy evaluation of a novel integrated hydrogen liquefaction structure using liquid air cold energy recovery, solid oxide fuel cell and photovoltaic panels

Abstract

High specific energy consumption (SEC) and its high cost of manufacturing are among the main problems in the hydrogen liquefaction industry. In this paper, an integrated structure for liquid hydrogen production using liquid air energy recycling, fuel cells, carbon dioxide power generation cycle, and photovoltaic (PV) panels is developed and exergetically assessed. To liquefy the hydrogen gas are utilized six compression refrigeration cycles with hydrogen and helium refrigerants. The compressed liquid air is used for the precooling of the hydrogen liquefaction process. After the cold energy recovery from liquid air, it is heated by the waste heat load of the refrigeration cycle and solid oxide fuel cell (SOFC) and then enters the gas turbine and fuel cell, respectively. The fuel cell output hot stream is used to supply heat to the power generation cycle and preheat the fuel cell inlet stream. This integrated structure generates 1,028 kg/h liquid hydrogen by receiving 60.79 kg/h natural gas and 5.559 MW power from solar panels under the climatic conditions of Yazd, Iran. The specific energy consumption of the hydrogen liquefaction process, SOFC efficiency, and carbon dioxide power generation cycle efficiency are obtained as 5.955 kWh/kgLH2, 62.96%, and 44.06%, respectively. Integrating the refrigeration structure with the process core is performed in the form of hot and cold composite diagrams. The exergy assessment indicates that the highest exergy destruction occurs in solar panels (81.37%), heat exchangers (7.60%), and turbines (4.73%), respectively. The sensitivity analysis demonstrates that the integrated structure exergy and SOFC efficiencies decrease to 52.9% and 62.3%, respectively when the inlet liquid air mass flow rate increases from 7,400 kg/h to 10,200 kg/h. The power supplied by solar panels and SEC of hydrogen liquefaction process increase up to 5,599 kW and 6.1 kWh/kg LH2, respectively with a decrease of pumped liquid air pressure from 80 bar to 40 bar.